Tight and Fractured Paleozoic Clastic Reservoirs; Workflow and Examples in a Challenging Complex Geological Environment
A fully integrated multidisciplinary workflow has been developed in O&G over the last decades to tackle the problem of tight clastic reservoirs which deliverability depends on the efficiency in terms of storativity, transmissivity (connectivity, permeability) of the multiscale fault and fracture patterns, and the interaction with the primary matrix porosity and permeability, deploying up to date technologies. In this paper the focus is on the new developments and applications of the fault and fracture network modeling. The existing multiscale methodologies in Data Driven, Model Driven and Process Driven DFFN (Discrete Fault and Fracture Network) modeling approaches are illustrated, and results of the newly developed DXM Protocol are shown which combine 3d spatial discontinuity modeling with geological relationships and drivers observed in Nature. The analyses and modeling of networks of discontinuities (fault zones, faults, damage zones, fracture swarms, Highly Persistent Fractures, joints, veins, stylolites, microfractures, etc. etc.) in clastic (both silicoclastic and carbonate) reservoirs has important implication, in conventional and non-conventional reservoir development, both the flow-enhancing properties as well as the sealing / compartimentalisation properties of these networks. Examples are presented of application of the workflow and technologies to appraisal and exploration in the areas of Tinrhert (Ilizzi-Berkine Basin) and M’Sari Akabli (Ahnet Basin) Blocks in Algeria, analogues of the well-known tight Gas producing Cambrian-Permian reservoirs of Saudi Arabia, Oman (e.g. Barik sst.), Qatar, and many other areas in the Middle East. These examples include the analyses of vintage and newly drilled well data (logs and cores, petrophysics, sedimentological facies and environment, and fracture characterization), vintage 2d and 3d seismic data, acquisition of 2d seismic data, and reprocessing of vintage 3d seismic data. The seismic interpretation and mapping went through all the classical phases of seismic to well tie, time mapping of key horizons, fault mapping, velocity modeling and structural mapping in the depth domain. An extensive exercise was performed on High Resolution satellite imaginary, especially acquired and elaborated, and was integrated, through GIS, with the seismic interpretation environment. The final result is a calculation of resources in terms of volumetrics and deliverability, and an extensive mapping of prospectivity for different reservoirs with connected risking and ranking. Various 3d seismic attribute analyses were applied to enhance the visibility of seismic and subseismic fault and fracture zones. A special data driven technique (FD5D) uses these observations to generate DFFN models on a subseismic scale. These models permit to evaluate the connectivity and heterogeneity of major Highly Persistent Fractures (HPF), and Damage Zones or Fracture Corridors, that can be important components of flow in the reservoir and contributing to compartmentalization or connectivity on reservoir block / drainage volume scale. The outlined principles are applicable in numerous areas in the Middle East in both carbonate and clastic environments. Additional to the Paleozoic reservoirs cited above, other examples are the Jurassic tight fractured carbonates of the Najmah/Sargelu Fm, such as in the Minagish field in Kuwait, and the “rubble carbonates” of the Cretaceous Mishrif Fm in the Awali Field in Bahrain, just to name a few. The multidisciplinary and multi-scale approach, using and evaluating numerous crucial parameters from different sources, provides a sound basis for the planning of exploration, appraisal and development wells in this challenging subsurface environment which shows multiple (some stacked) reservoirs characterized by dual porosity and dual permeability with highly complex three dimensional connectivity and heterogeneous drainage volumes, and provides clear directions for the future development and deployment of new technologies.
AAPG Datapages/Search and Discovery Article #90360 © 2019 AAPG Middle East Region Geoscience Technology Workshop, 3rd Edition of the Siliciclastic Reservoirs of the Middle East, Muscat, Oman, October 28-30, 2019